Industrial and home sewing machines basically employ a spring-loaded presser foot to exert a downward force on a fabric in its directed path of travel through the sewing machine elements during the sewing while the fabric is fed generally by a fabric feeding mechanism which may include serrated feed dogs positioned beneath and extending through a needle plate in cooperation with a presser foot. The presser foot is generally pivotally mounted on the sewing machine with the fabric-receiving forward end being upwardly inclined to facilitate fabric entry at the toe end. Usually increased force is exerted on the fabric being sewn at the heel of the presser foot with the presser foot being suitably hinged or pivoted and spring mounted on a presser foot arm.
Sewing transverse to a seam formed from a plurality of fabric plies is frequently troublesome particularly when relatively heavy denim fabrics and other coarse fabrics are sewn. The spring loaded presser foot assembly is displaced unevenly depending upon the presser foot assembly displacement and the nature of the helical spring modulus. The spring loading on the presser foot may vary depending upon manual adjustment of the spring loading but variations in the force exerted are inevitable and difficult to control across a wide range of fabric thicknesses. Changing or modifying the springs for applying proper force to the presser foot for various fabrics would be time consuming and troublesome.
Accordingly, an objective of this invention is to provide a sewing machine with a presser means that is displaceable between limits with a fluid means that communicates with the presser means for applying a predetermined and constant force to the presser means within the limits of presser means displacement and one that is readily adjustable depending upon the seam thickness in the fabric being sewn.
Another objective of this invention is to provide a sewing machine which incorporates a presser foot with a fluid actuated means for applying a predetermined and constant force to the presser foot which force may be readily adjusted.
Still another objective of this invention is the provision of a pneumatically-operated piston connected to a fabric presser means on a sewing machine for applying a predetermined and substantially constant force to the presser means that is displaceable between limits without incurring substantially increased forces throughout the displacement of the presser means during sewing across seams that are substantially bulky.
Other objectives and many of the attendant advantages of this invention will become more readily apparent to those skilled in the sewing machine art to which this invention is applicable including its use in conjunction with various types of fabric guide and control mechanisms when considered in conjunction with the accompanying drawing and detailed description of two preferred embodiments of the invention which are described without intending any limitations for their use in conjunction with other operating mechanisms connected directly or indirectly to foot treadles or other sewing machine actuating and deactivating mechanisms.